Forming protective inorganic coating on substrate

ABSTRACT

A method of forming an inorganic coating on a substrate is provided. The method includes applying on the surface of the substrate an aqueous inorganic coating composition comprising an alkali metal silicate and an inorganic condensed phosphate, which comprises applying before or after the application of the inorganic coating composition an effective amount of an aqueous curing agent solution of at least one compound selected from the group consisting of halides, sulfates, nitrates and organic acid salts of metals belonging to Groups II and III of Periodic Table and transition metals and ammonium halides, ammonium sulfate, ammonium persulfate, ammonium nitrate and inorganic acid salts of ammonium.

1Ob7 o AU 116 EX XR 397930055 United States Patent 1 Shodai et al.

[4 1 Feb. 19, 1974 FORMING PROTECTIVE INORGANIC COATING ON SUBSTRATEInventors: Masahiko Shodai, Takatsuki; Hideo Tomoltawa, Neyagawa, bothof Japan Matsushita Electric Works, Ltd., Kadoma City, Japan Filed: June17, 1971 Appl. No.: 154,176

Assignee:

Foreign Application Priority Data June 25, 1970 Japan 45-56277 US. Cl.117/47 R, 106/74, 117/47 R, 117/62,117/705,117/126 AF, l17/135.1,l17/148,117/169 A Int. Cl 844d 1/44, C01b 33/32 Field of Search 117/47R, 135.1, 705, 62, 117/169 A, 148,126 AF; 106/74 References Cited UNITEDSTATES PATENTS 9/1967 Paxton et al 117/169 A 2,944,916 7/1960 Evans1171169 A 3,423,229 1/1969 Kompanek et al 117/169 A 2,989,418 6/1961Harbaugh 117/169 A 3,232,782 2/1966 Shannon 117/62 PrimaryExaminer-MurrayKatz Assistant Examiner-William R. Trenor tq n tis wl qrfrm zrmstrq saw sns [57 ABSTRACT A method of forming an inorganic coatingon a substrate is provided. The method includes applying on the surfaceof the substrate an aqueous inorganic coating composition comprising anand an inorganic condensed J1me, whic comprises applying before or a terthe application of the inorganic coating composition an efiective amountof an aqueo curing agent solution of at least one compound semupconsisting of halides, sulfates, nitrates and organic acid salts ofmetalshelonging to Groups II and of Pen ic Table and transition metalsand ammonium halides, ammonium sulfate, ammonium persulfate, ammoniumnitrate and inorganic acid salts of ammonium.

4 Claims, No Drawings This invention relates to improvements in forminga protective inorganic coating on a substrate.

It is known to form a protective or corrosion-resistant coating on asubstrate such as metal, wood, slate, asbestos sheet, etc. Most ofconventional protective and/or anti-corrosive coatings of this kind areof organic ones such as asphalt, synthetic resins or the like. Theseorganic coatings have various drawbacks that they are inflammable, lowin thennal resistance, poor in hardness and not fully satisfactory inwater-resistance. Further, prior to providing such organic coating, thesurface must be cleaned. Even when an organic coating composition isapplied'on a clean surface, it is diflicult to obtain a firmly adherentcoating.

In order to overcome these drawbacks there hasbeen proposed an inorganiccoating composition comprising an alkali metal silicate and an inorganiccondensed phosphate.

Such inorganic coating composition, however, have some drawbacks amongwhich is that it takes a very long time to cure or to be insolubilizedat the room or normal temperature. Thus, it takes about 6 months or morebefore it is completely and satisfactBrily cured at the normaltemperature (15 30C.). Further during such long time exposure to the airthe alkaline component in the coating composition reacts with carbondioxide in the air to form carbonate(s) which deposits on the surface ofthe coating and therefore the appearance of the resulting coating isimpaired. Further, during such long time exposure, there is apossibility that the coating will be deteriorated due to erosion beforebeing completely cured or insolubilized. The curing may be promoted byheating but such is impractical and is impossible to practice in somecases. Further drawbacks of such inorganic coating are that it is notfully satisfactory in the resistance to water, resistance to weather,adherence and hardness.

Therefore it is an object of this. invention to provide an improvedmethod by which curing of such inorganic coating at the normaltemperature is-promoted.

Another object of this invention is to provide an improved method forforming a protective inorganic coating which is excellent in variousproperties such as water-resistance, weather-resistance, hardness, etc.and is firmly adherent to the surface of a substrate.

Other objects of this invention will be apparent from the followingdescription.

Briefly, the objects of this invention may be attained by a method forfonning an inorganic coating on a substrate by applying on the surfaceof the substrate a coating composition containing an aqueous solution ofan alkali metal silicate and a condensed inorganic phosphate,characterized by applying before or after the application of theinorganic coating composition an aqueous solution of at least onecompound selected from the group consisting of halides, sulfates,nitrates and organic acid salts of metals belonging to groups II and IIIof Periodic Table and Transition metals and ammonium halides, ammoniumsulfate, ammonium persulfate, ammonium nitrate and organic acid salts ofammonium.

In carrying out the method of this invention, any inorganic coatingcomposition which comprises an alkali metal silicate and a condensedinorganic phosphate and which may be cured or insolubilized by chemicalreaction may be used. However, it is preferable to employ an inorganiccoating composition which comprises an aqueous solution comprising analkali metal silicate and a condensed phosphate prepared by heating amixture of (A) a phosphate having an average composition formula:

MO'xP OfyI-LO wherein M represents a metal selected from the groupconsisting of Al, Mg, Ca, Mn, Zn, Fe and Cu, the atomic ratio MI? is0.25 1.0, each ofx and y is a real number and (B) a spine] type doubleoxide of (a) one metal selected from those belonging to Group ll ofPeriodic Table and (b) at least one metal selected from transitionmetals and metals belonging to Group IV of Periodic Table.

As mentioned above thephosphate to be used is represented by thefollowing formula:

wherein M is a metal selected from the group consisting of Ca, Mg, Al,Cu, Fe, Mn and Zn, the atomic ratio MI? is 0.25 1.0, and each of xand yis a real number. Preferably M consists of or mainly of Al. The value xmay be determined from 0.25 5 M/P 5 1.0, but the value y variesdepending upon the particular product and ambient moisture conditionbecause the degree of hydration varies. Thus the phosphate may be one ora mixture of two or more of commercially available primary phosphates ofCa, Mg, Al, Cu, Fe, Mn and Zn. It is pref- .erable however that thephosphate consists of or mainly of primary aluminium phosphate, whichmay be added with or partly replaced by one or more of primaryphosphates of Mg, Ca, Mn,Fe, Zn and Cu. If desired, the primaryphosphate may be mixed with one or more of secondary phosphate such as2Al,0;,'3P,O,'3H,O, 2CaO'P,O 'l-l,O, 2Mg0P,O,-l-l,0, etc;sesquiphosphates such as Al,0,'2P,0,'3l-l,O; and Cal-l,P,O,, etc. Evenin a form of mixture, it should satisfy the above formula.

The above mentioned phosphate is mixed and reacted with a double oxidewith spiral structure and then the mixture is heated to form a condensedphosphate."

The double oxide to be mixed with the phosphate must have the so-calledspinel structure. The metals forming the double oxide should compriseboth (a) one metal selected from those belonging to Group ll of PeriodicTable and (b) at least one metal selected from transition metals andmetals belonging to Group IV of Periodic Table. Preferable metals of (a)are zinc and magnesium, while preferable metals of (b) are Ti, Fe, Mn,Co and Cr.

The double oxides may be prepared in any known manner. Thus, forexample, one metal compound selected from the group consisting ofoxides, hydroxides, carbonates and organic acid salts of metalsbelonging to Group II of Periodic Table is mixed with at least one metalcompound selected from the group consisting of oxides, hydroxides,carbonates and organic acid salts of metals belonging to Group IV ofPeriodic Table and transition metals. The mixture is calcinated at atemperature from 700C. to 1,200C. for 2 10 hours to form a double oxidewith spinel structure. The proportions of the various metal compoundsand the temperature and time for the calcination are determined in orderto form double oxides with spinel structure. These conditions of coursevary depending upon the particular metal compounds, but can be easilydetermined by referring to known literatures relating to the productionof spinel type double oxides. In any case the metal compounds to be usedshould be those which can form oxides upon the above mentionedcalcination.

The above mentioned phosphate and double oxide are mixed together andthe mixture is heated to prepare the condensed phosphate. Generally, thedouble oxide is used in an amount of 0.2 1.5 parts by weight per part ofthe phosphate. The heat treatment conditions may vary over a wide rangedepending upon the particular apparatus (type of furnace) and particlesize of the materials to be heated. However, generally, the mixture isheated at a temperature of 120- 350C. for 30 minutes to hours,preferably 2 7 hours.

After the heat treatment or calcination the resulting solid mass(condensed phosphate) is pulverized into fine powder.

The condensed phosphate powder is then mixed with an aqueous solution ofan alkali metal silicate, e.g., lithium silicate, potassium silicate,sodium silicate. 1f desired the alkali metal silicate may be modified byan al- 3 am, calcium carbonate, gypsum, furnace waste, etc. The fillermay be added in an amount of 15 percent by weight or less based on thetotal amount of the solid component in the composition.

The aqueous coating composition which is in the form of slurry or pastemay be applied to the surface of an article to be protected in anysuitable manner such as spraying, brush-painting roller-coating,airlessspraying, etc. Usually, the inorganic coating composition isapplied in such amount that about 70-150 g. (as dried solid) of thecoating will cover a square meter of the substrate surface.

The coating composition of this invention is curable at the roomtemperature but it takes a very long time to cure at the normaltemperature (15 30C.). In order to promote cure it is necessary toeffect moisturecure or thermal cure.

However, such moisture-cure or thermal cure is not convenient or notpractical.

' Therefore, according to the invention, a special but simple measure istaken to promote the curing, which is the novel and essential feature ofthe invention.

Thus, according to the invention, before or after applying the inorganiccoating composition, there is applied an aqueous solution (sometimesreferred to as "curing agent) of at least one compound selected from thegroup consisting of (l) halides, sulfates, nitrates and organic acidsalts of metals belonging to Group II and Group III of Periodic Tableand transition metals and (2) halides, sulfate, persulfate, nitrate andorganic acid salts of ammonium.

Amoung the above compounds (1) and (2), most preferable ones arepotassium alum, ammonium alum,

aluminum nitrate, aluminum chloride, ammonium persulfate. Magnesiumchloride, calcium chloride, zinc chloride, ammonium oxalate, ammoniumacetate, ammonium sulfate and ammonium nitrate are also preferable ones.A mixture of two or more of these compounds may also be used.

According to one embodiment of this invention the above aqueous solutionW222i! the surface of a substrate ore e inorganic Sl icatephosphate typecoating composition is applied. According to another embodiment of theinvention, the surface of a substrate is first coated with the inorganiccoating composition and then on the coated layer there is applied theabove mentioned curing agent. It is preferable, however, to apply thecuring agent both before and after the application of the inorganiccoating composition.

The molar concentration of the above mentioned compound (1) and/or (2)in the aqueous solution (curing agent) may be about 0.25 3 mols perliter of the solution. Preferably, the molar concentration is about 0.251 mol per liter in case of sub-coating and is about 1 3 mols per literin case of top-coating. If the molar concentration exceeds the abovementioned upper limit there is a tendency that cracks are formed on theinorganic coating due to excessively rapid curing.

In any of sub-coating (pretreatment) and top-coating (after-treatment),it is preferable that the amount of application of the curing agent issuch that about 0.001 0.5 mol, preferably about 7 10 g. of the compound(1) or (2) is present per square meter of the substrate surface or theinorganic coating already applied.

The application of the curing agent may be conducted in any suitablemanner, such as spraying, brushing or dipping.

In case of sub-coating or pre-treatment, it is preferable that theinorganic coating composition is applied after the previously appliedcuring agent is substantially dried because if the latter layer is stillwet the application of the inorganic coating composition thereupon willcause a rapid or violent reaction resulting in the formation of cracks,wrinkles or the like in the cured coating. Similarly, in the case of thetop-coating or after-treatment, it is preferable that the aqueous curingagent is applied after the previously applied inorganic coatingcomposition layer has been dried because if the aqueous curing agent isapplied on the layer of the inorganic coating composition while thelatter is still wet there would occur rapid or violent reaction which isundesirable as explained above. Thus, in any case, it is preferable thateither one of the inorganic coating and curing agent to be contactedwith each other is in substantially dry state and the other is in wetstate. If desired a small amount (e.g. about 5 30 parts by weight basedon the aqueous curing agent) of a high boiling point liquid (e.g.glycerine, ethylene glycol, etc.) miscible water may be added to theaqueous curing agent to control the rate of drying of the latter.

When the inorganic coating solution is applied on the substratepretreated with the curing agent in the above mentioned manner, thecuring of the inorganic coating is promoted even at the normal or roomtemperature (15 -30C.) and there is obtained a firmly adherent, solid,hard and insolubilized inorganic coating with excellent resistances towater and weather within a relatively short period of time (e.g. 1 2days). Similar result is obtained when an inorganic coating solution isfirst applied and after air-drying the same the curing agent is appliedon'the dried surface of the inorganic coating which has not yet beencured. It is of course preferable to apply the curing agent both beforeand after the application of the inorganic coating composition.

The method of this invention can be applied to any substrate. However,when the curing agent is applied prior to the application of theinorganic coating composition it is preferable that the surface of thesubstrate is such that can retain or held the curing agent or solution.Thus, those substrates having porous surfaces such as plates, sheets orthe like of asbestos, cement, slate, wood, etc. are preferable. in suchcase, the curing agent is effectively impregnated or held in the poroussurface of the substrate and therefore more firmful bonding of thesurface with the subsequently applied inorganic coating is facilitated.

By the above curing, the coated composition is set or cured and becomesa hard, firmly adherent, waterresistant anti-corrosive coating on thesurface of an article. The appearance of the coating is enamel orporcelain like. Further, the resulting coating is not only hard andanticorrosive but also excellent in resistance to heat, flame, water andweather, and is stable for a prolonged period of time.

This invention will be illustrated in the following Examples wherein allparts are by weight.

Example 1 A flexible slate (thickness 3 mm.) was first coated with a 1:1mixture of an aqueous solution containing 1 mol/liter of aluminumchloride and an aqueous solution containing 0.5 mol/liter of ammoniumpersulfate of provide a coverage of 9 gr. of aluminum chloride and ofammonium persulfate per square meter. The coated slate was left to standovernight at the room temperature (C.) to dry. Then the pretreated slatesurface was coated with an inorganic coating composition to provide acoverage of 120 g. (as dry solid) per square meter. The inorganiccoating composition was prepared as follows. A mixed phosphate (M/P 0.4)consisting of 5 parts of primary aluminum phosphate and 5 parts ofprimary magnesium phosphate was mixed with 2 parts of zinc titanate. Themixture was calcinated at 130C. for 4hours to obtain a condensedphosphate. The condensed phosphate was pulverized and 2 parts thereofwermefwith 3 parts of sodium silicate (50 percent aqueous solution), one"pa'rfbf water and 0.4 part of white pigment (titanium white) to obtainthe coating composition.

The coated slate was air-dried at about 20C. for 2- days to obtain curedinorganic coating, the properties of which was as follows:

Appearance: Good Adherence: Cross-cut test (2 mm. X 2 mm.)

Hardness: Scratch hardness by Clemen's hardness tester I50 gr.

20 days (at 20C.)

20 hours (boiling water) Weather-OMeter, no change after i000 hours.

Water resistance: Hot water resistance: Weather resistance:

Example 2 vide a coverage of 10 g. of zinc nitrate and ammonium alum persquare meter. After about 5 hours of airdrying at about 20C., aninorganic coating composition was applied on the pretreated surface toprovide a coverage of g. (as dry solid) per square meter. The inorganiccoating composition was prepared as follows. A mixed phosphate (M/P 0.5)consisting of 4 parts of primary zinc phosphate, 5 parts of primaryaluminum phosphate and 1 part of calcium pyrophosphate was mixed with 4parts of MnFe,O., (spinel type double oxide) and the mixture wascalcinated at C. for 4 hours to obtain a condensed phosphate. Theresulting condensed phosphate mass was pulverized and 5 parts thereofwere mixed with 7 parts of sodium silicate (50 percent aqueoussolution), 2 parts of water and one part of white pigment (titaniumwhite).

The coated slate was air-dried at about 20C. for 2 days to form a curedinorganic coating which has excellent properties similar to thoseobtained in Example 1 except that the Clemens hardness was 120 gr.

The same procedure was repeated except that no pre-treatment wasconducted. No noticeable curing of the coating occurred and the coatingwas dissolved away in 1 minute when dipped in water at 20C.

Example 3 Appearance: Good Adherence: -Cross-cut test (2 mm. X 2 mm.)

Hardness: Scratch hardness by Clemens hardness tester I50 gr.

l5 days (at 20C.)

l5 hours (boiling water) Weather-O-Meter, no change after 750 hours.

Water resistance: Hot water resistance: Weather resistance:

The same procedure was repeated except that the pre-treatment was notconducted. No noticeable curing of the coating occurred, and the coatingwas dissolved away in 1 minute when dipped in water at 20C.

Example 4 A mixed phosphate (M/P 0.4) consisting of 55 parts of primaryaluminum phosphate and 45 parts of primary calcium phosphate was mixedwith 90 parts of magnesium titanate and the mixture was calcinated at C.for 5 hours. The resulting condensed phosphate mass was pulverized and50 parts thereof were mixed with 50 parts of sodium silicate (50 aqueoussolution) and 100 parts of water to obtain an inorganic coatingcomposition. The coating composition was applied on the surface of aslate to provide a coverage of 95 g. (as dried solid) per square meter.The coated slate was allowed to air dry at the room temperature (20C.)for 4 hours. Then, a curing agent, i.e., an aqueous solution containing0.5 mol/liter of calcium chloride and 1 percent by weight of ethyleneglycol was applied on the dried coating to provide a coverage of 8 g.

of calcium chloride per square meter of the surface. The top-coatedslate was air-dried at about 20C. for 2 days. The resulting curedinorganic coating had the following properties:

Adherence: Cross-cut test 100/100 Scratch test (drawing test) 8Hardness: Scratch hardness by Clemen's hardness tester 200 gr. Taborabraser 300 rounds, base not exposed in the abraded track 20 days (at20C.) 20 hours (boiling water) Wear-resistance:

Water resistance: Hot water resistance:

Example A slate was first coated with a curing agent, i.e., an aqueoussolution containing 1 mol/liter of aluminum chloride to provide acoverage of 9 g. of aluminum chloride per square meter. The surface wetslate was air-dried at about 20C. for 6 hours. Then the pretreatedsurface was coated with an inorganic coating composition to provide acoverage of I00 gr. (as solid) per square meter. The coating compositionwas prepared as follows. A mixed phosphate (M/P 0.5) consisting of 50parts of primary aluminum phosphate, 10 parts of calcium pyrophosphateand 40 parts of primary zinc phosphate was mixed with 40 parts of bariummanganate, and the mixture was calcinated at 140C. for 4 hours. Theresulting condensed phosphate was pulverized and 60 parts thereof weremixed with 40 parts of potassium silicate (solid content 50 percent) and100 parts of water to obtain the inorganic coating composition.

The above coated slate was air-dired at about C. for one day and thenthe sa c rin agent as above was applied on the dried coating su ace toprovide a coverage of 8 g. of aluminum chloride per square meter. Thetop-coated slate was air-dried at about 20C. for 2 days. The resultingcured coating had properties comparable with those in Example 4, exceptthat the scratch hardness was higher, i.e., 350 g.

Example 6 The procedure of Example 4 was repeated except that an aqueoussolution containing 0.5 mol/liter of zinc nitrate was employed as acuring agent instead of the calcium chloride solution. The properties ofthe resulting cured inorganic coating were as follows:

Adherence: Cross-cut test 100/100 Scratch test (drawing test) 6 Scratchhardness by Clemen's hardness tester gr.

Tabor abraser 300 rounds, base not exposed in the abraded track 10 days(at 20C.)

10 hours (boiling water) Hardness:

Wear resistance:

Water resistance: Hot water resistance:

The same procedure was repeated except that the curing agent was notapplied. No noticeable curing of the inorganic coating occurred and thecoating was dissolved away within 1 minute when dipped in 'water at 20C.

What we claim is:

l. A method of forming an inorganic coating on a substrate comprisingapplying to the surface of said substrate i. an aqueous inorganiccoating composition comprising 0.3 to 1.5 parts of an alkali metalsilicate and one part of a condensed phosphate prepared by heating amixture of (A) a phosphate having an average composition formula:

wherein M represents a metal selected from the group consisting of Al,Mg, Ca, Mn, Zn, Fe and Cu, the atomic ratio M/P is 0.25 1.0, each of xand y is a real number and (B) a spinel type double oxide of (a) onemetal selected from those belonging to Group 11 of Periodic Table and(b) at least one metal selected from transition metals and metalsbelonging to Group IV of Periodic Table, the ratio of the component (B)being 0.2 1.5 parts by weight per part of the component ii. 0.001 to 0.5mol per square meter of said surface of a curing agent of potassiumalum, ammonium alum, aluminum nitrate, aluminum chloride, ammoniumpersulfate, magnesium chloride, calcium chloride, zinc chloride,ammonium oxalate, ammonium sulfate or ammonium nitrate in an aqueoussolution; and

iii. drying the thus treated substrate.

2. A method as claimed in claim I wherein the aqueous curing agentsolution is first applied on the substrate surface, drying the same andthen applying the inorganic coating composition thereon.

3. A method as claimed in claim 1 wherein the inorganic coatingcomposition is applied first on the substrate surface, drying the sameand then applying the aqueous curing agent solution thereon.

4. A method of claim 1, wherein said substrate is slate.

asses:

2. A method as claimed in claim 1 wherein the aqueous curing agentsolution is first applied on the substrate surface, drying the same andthen applying the inorganic coating composition thereon.
 3. A method asclaimed in claim 1 wherein the inorganic coating composition is appliedfirst on the substrate surface, drying the same and then applying theaqueous curing agent solution thereon.
 4. A method of claim 1, whereinsaid substrate is slate.